Unidirectional Propagation Of Polarization Independent Light Waves In Photonic Crystal Waveguide Heterostructures

As an information carrier,photons are transmitted in the chip,which has a series of advantages,such as low energy consumption,large information capacity and high bandwidth.Photons can be used for information transmission and light quantum calculation in the system on nano optical chip.In the process of information transmission and processing,asymmetric optical transmission device is of great significance,which can realize one-way transmission of light wave and suppress the interference of reverse signal.There are two kinds of asymmetric transmission devices,reciprocal and nonreciprocal.Nonreciprocal asymmetric transmission devices require magnetic field applied in micro nano structure to realize asymmetric optical transmission using magneto-optical effector high intensity light field applied using nonlinear effect,so it is not easy to realize integration on photonic chip.In contrast,reciprocal asymmetric transmission devices can be designed according to different principles and have better diversity and tunability,such as photonic crystal(PhC)directional band gap,grating diffraction,surface plasmon,metamaterial,etc.However,there are still some limitations,such as low transmission efficiency,single polarization state of light wave and serious dissipation.Circularly polarized light(CPL)and radially polarized light(RPL)have unique polarization characteristics compared with linearly polarized light,which can not only transfer optical signal,but also have photon spin state,which can enhance the capacity of optical communication channel.Circularly polarized light and radially polarized light are formed by the linear superposition of TE and TM,so their complete photonic band gap is defined as the realization of photonic band gap in all directions for linearly polarized light along te and TM directions in a certain frequency range,and the transmission of light in this frequency range is prohibited in the photonic crystal structure,which is also an important characteristic of photonic crystal.In principle,the optical waveguide based on the principle of complete photonic band gap can realize the transmission of circularly or radially polarized light.However,most of the current photonic band gap waveguide structures are based on the transmission of linearly polarized light TE or TM,which have some problems,such as single polarization state,low transmission transmittance and weak spatial localization of light wave.Combined with the influence factors of photonic crystal full photonic band gap,we choose the integrable materials and relatively appropriate structure to design the optical quantum device with the largest full photonic band gap.Complete photonic band gap is defined as the realization of photonic band gap in all directions for linearly polarized light along TE or TM direction in a certain frequency range,or the realization of photonic band gap in all directions at the same time.In principle,an optical waveguide based on complete photonic band gap principle is designed,which can realize the unidirectional transmission of TE polarized light,TM polarized light,circularly polarized light or arbitrary linearly polarized light.1.Unidirectional transmission of TE / TM in optical waveguide heterostructuresAn optical waveguide heterostructure based on complete photonic band gap is designed.The structure is composed of a new material gallium arsenide and a high refractive index material germanium.The triangular lattice with circular air holes is used.At the same time,in order to enhance the spatial localization of light wave,the width of PhC1 waveguide on the left side is to remove a row of air holes.In order to improve the unidirectional transmission performance of the device,PhC2 waveguide is to remove three empty holes Two sets of parameters are designed to realize the unidirectional transmission of TE polarized light and TM polarized light in the optical waveguide heterostructure.For TE polarized light,the complete photonic band gap of the whole device is 258.909 nm,the forward transmittance of TE polarized light at 1550 nm is increased to more than 0.8,the complete photonic band gap of TM polarized light is 713.627 nm,and the forward transmittance of 1550 nm TM polarized light is greater than 0.7.2.Unidirectional transmission of circularly polarized light waves in optical waveguide heterostructuresIn this chapter,a two-dimensional photonic crystal planar waveguide heterostructure with complete photonic band gap is used to realize the asymmetric optical transmission of circularly polarized light.At the same time,a reciprocal optical waveguide asymmetric transmission device is realized by using the light field divergent microcavity combined with the total reflection principle to limit the reverse transmission light.At the same time,the working principle of the device can be applied to the asymmetric light transmission of arbitrary polarized light.Firstly,the material of the photonic crystal is selected and the structure is optimized by introducing the line defect.The forward high transmission light transmission of TE and TM linear polarization state in the photonic band gap is realized.On this basis,circularly polarized light is introduced by linear superposition method to achieve high forward transmittance of circularly polarized light.At the same time,the asymmetric transmission of circularly polarized light based on the complete photonic band gap is realized by using the divergence of light field and the total reflection of interface to suppress the reverse light transmission.The designed structure can achieve forward transmission of 0.726 and transmission contrast of 0.568 in the wavelength range of 1550 nm.The asymmetric transmission devices can be fabricated by using the existing complementary metal oxide semiconductor(CMOS)nanofabrication process.Therefore,it can be widely used in optical communication and quantum computing.3.Unidirectional propagation of radially polarized light waves in optical waveguide heterostructuresIn this chapter,we design a two-dimensional photonic crystal waveguide heterostructure which can realize the unidirectional transmission of radially polarized light.We combine the radially polarized light with the two-dimensional structure.On the left side of the heterostructure,PhC1 uses low refractive index material silica background embedded with germanium dielectric column,and on the right side,PhC2 uses silicon background air hole structure The forward transmittance is 0.35 and the transmission contrast is 0.99.